The present invention relates to compressors employed in, for example, air conditioners for vehicles. More particularly, the present invention relates to compressors that suppress the production of vibrations and noise.
A known type of compressor employs a swash plate, which is secured to a drive shaft and coupled to pistons. In a swash plate compressor, the rotation of the swash plate is converted to the reciprocation of the pistons to compress refrigerant gas. Screw compressors, which employ a pair of screw-like rotors to compress fluid, are also known in the prior art.
In both swash plate and screw compressors, fluctuations of the torque applied to the drive shaft or the rotor and flucutations of the compression reaction forces acting on the swash plate or the rotor during compression produce vibrations. The vibrations increase the noise level of the compressor.
To reduce vibrations and suppress noise, the employment of dampers has been proposed. For example, Japanese Unexamined Patent Publication No. 5-33787 describes a screw compressor having two rotors 70 as shown in FIG. 5. One of the rotors 70 is supported by a shaft 71. A damper 72, which is a conventional dynamic damper, is engaged with the shaft 71. The damper 72 includes a spring 73, which is connected with the shaft 71, and a weight 74, which is coupled to the spring 73. The damper 72 has a natural frequency that is determined by the spring constant of the spring 73 and the mass of the weight 74. The natural frequency of the damper 72 is about the same as the maximum axial vibrating frequency of the rotor 70. In other words, the frequency of the damper 72 and the frequency of the rotor 70 are in the same range. Therefore, the vibrations of the damper 72 offset the axial vibrations of the rotor 70 and thus reduce noise-producing vibrations.
The above publication also teaches the employment of a rubber body in lieu of the spring 73. In the same manner as when using the spring 73, if the axial vibrating frequency of the rotor 70 is included in the same range as the natural frequency of the damper, vibrations are reduced.
However, despite the drastic decrease in the frequency peak of the rotor 70, the rotor 70 would still vibrate axially when its vibration frequency is outside the natural frequency range of the damper 72. Thus, the reduction of vibrations is insufficient.
If the damper employs the rubber body, the natural frequency of the damper is varied greatly by the temperature of the rubber body. This is because the spring constant of the rubber body, which determines the natural frequency of the damper, varies in accordance with the temperature.
Compression reaction forces fluctuate the torsion acting on the rotor 70 and produce vibrations (torsional vibrations). Such torsional vibrations can be reduced by a dynamic damper having an elastic body, which serves as a spring acting in the torsional direction, and a weight. However, this damper, which reduces torsional vibrations, has the same deficiency as the damper 72, which reduces axial vibrations, in that the reduction of vibrations is insufficient.
Axial and torsional vibrations of the drive shaft and the swash plate also occur in swash plate compressors. However, it is apparent that the application of the damper employed in the above screw compressor would not sufficiently reduce vibrations in a swash plate compressor.